<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <input type="text" id="txt">
        <p id="show"></p>
    </div>
    <script type="text/javascript">
        var obj = {}  
        Object.defineProperty(obj, 'txt', {    
            get: function() {      
                return obj    
            },
                set: function(newValue) {      
                document.getElementById('txt').value = newValue
                document.getElementById('show').innerHTML = newValue    
            }  
        })
        document.addEventListener('keyup', function(e) {    
            obj.txt = e.target.value  
        })
    </script>
</body>

</html>